US 7336452 B2
In magnetic read heads based on bottom spin valves the preferred structure is for the longitudinal bias layer to be in direct contact with the free layer. Such a structure is very difficult to manufacture. The present invention overcomes this problem by introducing an extra layer between the bias electrodes and the free layer. This layer protects the free layer during processing but is thin enough to not interrupt exchange between the bias electrodes and the free layer. In one embodiment this is a layer of copper about 5 Å thick and parallel exchange is operative. In other embodiments ruthenium is used to provide antiparallel exchange between the bias electrode and the free layer. A process for manufacturing the structure is also described.
1. A magnetic read head, comprising:
a GMR stack whose topmost layer is a magnetically free layer;
on said free layer, a buffer layer having a trapezoidal cross-section whereby said buffer layer further comprises a central area, of uniform thickness and having a width, that has two opposing parallel edges and, abutting said edges, opposing side areas whose thickness tapers off uniformly to zero over a distance from each of said edges;
on said buffer layer, excluding said central area, and on said free layer, a soft ferromagnetic layer;
on said soft ferromagnetic layer, an antiferromagnetic layer;
on said antiferromagnetic layer, a conductive lead layer; and
on all of said central area, a cap layer.
2. The read head described in
3. The read head described in
4. The read head described in
5. The read head described in
6. The read head described in
7. The read head described in
8. The read head described in
This is a division of patent application Ser. No. 10/116,984, filing date Apr. 5, 2002 now U.S. Pat. No. 6,842,969, Patterned Exchange Bias Gmr Using Metallic Buffer Layer, assigned to the same assignee as the present invention, which is herein incorporated by reference in its entirety.
The invention relates to the general field of magnetic read heads with particular reference to providing longitudinal bias to bottom spin valves.
The principle governing the operation of the read sensor in a magnetic disk storage device is the change of resistivity of certain materials in the presence of a magnetic field (MR or magneto-resistance). Magneto-resistance can be significantly increased by means of a structure known as a spin valve. The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The key elements of what is termed a bottom spin valve, as seen in
Although the layers enumerated above are all that is needed to produce the GMR effect, additional problems remain. In particular, there are certain noise effects associated with such a structure. As first shown by Barkhausen in 1919, magnetization in a layer can be irregular because of reversible breaking of magnetic domain walls, leading to the phenomenon of Barkhausen noise. The solution to this problem has been to provide operating conditions conducive to single-domain films for the GMR sensor and to ensure that the domain configuration remains unperturbed after processing and fabrication steps. This is most commonly accomplished by giving the structure a permanent longitudinal bias provided by two opposing permanent magnets.
One way to implement this is with an exchange biased magnetic layer as also shown in
In the case of bottom spin valves, it would, in theory, be ideal if the AFM layer could be placed directly in contact with the free layer, with the sensor region being left uncovered to sense the external media field. This is illustrated in
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,266,218, Carey et al. show a MR with a Bottom Spin Valve and patterned exchange process while Pinarbasi describes a MR with a Bottom SV and buffer layer in U.S. Pat. No. 6,275,362. U.S. Pat. No. 6,310,751 (Guo et al.) shows a pattern exchange for a DSMR, U.S. Pat. No. 6,308,400 (Liao et al.) also discloses a pattern exchange for a DSMR and U.S. Pat. No. 5,637,235 (Kim) discloses a Bottom SV.
It has been an object of at least one embodiment of the present invention to provide a magnetic read head that includes narrow track width, good longitudinal stability, good GMR response, and ease of manufacturability.
Another object of at least one embodiment of the present invention has been to provide a process for manufacturing said read head.
These objects have been achieved by introducing an extra layer between the bias electrodes and the free layer. This layer protects the free layer during processing but is thin enough to not interrupt exchange between the bias electrodes and the free layer. In one embodiment this is a layer of copper about 5 Å thick and parallel exchange is operative. In other embodiments ruthenium is used to provide antiparallel coupling between the bias electrode and the free layer. A process for manufacturing the structure is also described.
The present invention discloses a device that has a patterned exchange biasing structure that makes use of the exchange coupling through a metallic buffer layer placed on top of the GMR sensor for ease of manufacturability.
This structure is built by deposition of a GMR stack that is terminated by a buffer layer such as Cu, Ag, Ru, or Rh and a specular reflection layer such as Ta or an oxidation protection layer such as Ru or Rh or any combination thereof. The track (or central area) is defined by photolithography using a liftoff technique. Its width is between about 0.05 and 0.25 microns. Ta is removed by RIE and the Cu spacer is removed by gentle sputter etching. If Ru or Rh is used instead of, or in addition to, Ta they would be removed by ion beam or sputter etching. The total Cu thickness is typically between about 2 and 20 Å, with about 5 Å being preferred, so sufficient exchange pinning remains between free layer 12 and added ferromagnetic layer 32.
Following sputter etching of the Cu, a stack of additional ferromagnetic material of the order of 0.25-1 times the free layer thickness is deposited. This layer is any suitable material such as NiFe, CoFe, or Co. It is between about 5 and 75 Angstroms thick. Then, AFM 17, such as PtMn, NiMn or IrMn, is deposited to provide exchange pinning to the tail region. This is the area over which the thickness of the buffer layer tapers off uniformly to zero. It is typically between about 0.01 and 0.20 microns wide.
The antiferromagnet deposition angle is preferably somewhat shallower than for the ferromagnet to facilitate coverage of layer 32 by layer 17. The deposition concludes with leads and photoresist lift-off. The entire structure is then annealed in a longitudinal field to provide exchange pinning from AFM 17 to added ferromagnet 32 and the free layer. The exchange pinning from the antiferromagnet to the added ferromagnet is typically of the order of 200-500 Oe. The exchange pinning across the Cu interface is also within the same range or could be slightly lower. In both these structures the magnetization of the free layer and of the added ferromagnet are parallel to one another (along the longitudinal anneal directions). A closeup view of the junction area of
A second embodiment of the present invention is shown in
One shortcoming of the above embodiment is the fact that there is no excess moment from the tail region since layers 12 and 32 are annealed at similar temperatures. In fact the total moment of the tail region is lower than the free layer moment. This problem is overcome in a third embodiment of the present invention that utilizes a laminate of two ferromagnetic layers 61 and 63 between which is sandwiched second Ru layer 62, as part of the tail region, as shown in
The fourth embodiment of this invention is a patterned exchange type device illustrated in